Sensors are utilized in a number of applications, including various medical, commercial and industrial applications. For example, it is often necessary to monitor pressure and/or to detect flow rates in medical applications and processes.
One area where pressure sensors, for example, find particular usefulness is in the area of hemodialysis applications. In such medical procedures, a dialysis machine is utilized to clean wastes from the blood after the kidneys have failed. The blood travels through tubes to a dialyzer, a machine that removes wastes and extra fluid. The cleaned blood then goes back into the body.
A known-type dialysis machine comprises a first blood circulation circuit and a second circulation circuit for the dialysate liquid. The first circuit and the second circuit are connected to a filter for conveying, respectively, the blood and dialysate liquid through the filter, which is provided with a semi-permeable membrane separating the blood from the dialysate liquid. The first circuit is provided with a container, known as a drip chamber, into which the blood is supplied from a first tract of the first circuit, and drips and collects on the bottom of the container, thence to enter a second tract of the first circuit.
The container has the function of preventing air from becoming trapped in the blood in the form of bubbles, which might cause embolisms once the treated blood is returned to the cardiovascular system of the patient. To guarantee the safest possible treatment the blood level in the container must be maintained within an optimum range of values, below which the possibility of creating air bubbles in the blood returning to the patient exists, and above which the pressure increases to unacceptable values which are dangerous for the patient. Thus, the ability to monitor pressure in such a setting is critical to a proper, safe, and successful dialysis treatment.
One type of dialysis application is disclosed in U.S. Pat. No. 6,695,806, entitled “Artificial Kidney Set with Electronic Key,” which issued to Gefland et al on Feb. 24, 2004 and is incorporated herein by reference. Another type of dialysis application is disclosed in U.S. Pat. No. 6,887,214, entitled “Blood Pump Having a Disposable Blood Passage Cartridge with Integrated Pressure Sensors,” which issued to Levin et al on May 3, 2005 and is incorporated herein by reference. It can be appreciated that U.S. Pat. Nos. 6,695,806 and 6,887,214 are referenced herein for general background and edification purposes only and are not considered limiting features of the embodiments described herein.
Dialysis machines historically have utilized sets of disposable components that are assembled from various parts produced by different manufacturers. This allowed flexibility, but also resulted in certain disadvantages. Joints between component parts, for example, may leak, allow ingress of air and facilitate blood clotting. A high skill was required by hospital nurses and technicians to assemble the tubes, connectors, filters and accessories and then load them correctly into pumps, bubble detectors, pressures sensors and other elements of a dialysis machine. In the setting of a chronic dialysis center such practices were acceptable. In an acute setting, however, such an Intensive Care Unit (ICU) of a hospital, the complexities of dialysis machines can become an impediment.
As a result, the use of mechanical fluid removal in the ICU, emergency rooms and general floors of a hospital has been limited. Some manufacturers have released sophisticated dialysis equipment based on the use of an integrated set of disposable dialysis components in which the tubing, filter and accessories are bonded together and no assembly is required. In such a device, the filter, sensor interfaces and four dedicated pump segments (for blood, dialysate, replacement solution and effluent) can be mounted on a flat plastic cartridge to simplify the loading of the dialysis pumps. Such a dialysis system has been marketed as offering an integrated system for continuous fluid management and automated renal replacement therapy blood.
While such devices do offer significant advantages, such equipment also has a number of deficiencies. One deficiency is that although such systems provide for a set of disposable dialysis components that are continuous and bonded together, the system does not present a smooth blood path, but incorporates elements that create stagnant and slow moving blood zones. In such blood zones clots are likely to form. Such devices may also employ an interface to pressure sensors that is relatively inaccurate, unreliable and requires maintenance. There is thus a need for an improved design of the blood flow dialysis set that is simple to use, requires no maintenance or special training, and also has an improved performance over existing sets of disposable components utilized in such dialysis machines.
Additionally, such dialysis machines do not integrate pressure sensors. Instead, these types of dialysis devices integrate pressure “pods” shaped as domes. The interface surface of a pod can be made from a silicon membrane approximately one inch in diameter. When mounted on such a dialysis machine, the pods interface with the permanently installed pressure sensors that form a part of the machine. The interface is sealed by a rubber gasket so that the pod membrane serves as a lid on the pressure transducer cavity. When in operation, blood and other fluids flow through the pods and come in contact with the membrane.
Pressure pods provide a means to measure the pressure of blood and other fluids flowing outside an interface surface. When the pressure inside the pod is increased, the diaphragm stretches and thereby compresses the air inside a transducer cavity. As a result, pressure in the bloodline or a fluid line can be measured. The pod membrane serves as a barrier between the blood and potential contamination from the environment, as is similar to the clinical invasive vascular blood pressure measurements. This method, although functional, has several deficiencies.
First, to be accurate such pods need to be positioned perfectly when the pressure inside is atmospheric. Over time, if there is even a miniscule leak on the transducer side of the membrane, the pod will creep and gradually stop transmitting pressure accurately because of the tension in the membrane. Second, stretchable membranes and air filled transducer cavities add compliance to the circuit. Compliance is a delay in a pressure measurement due to the time required to stretch the pods and compress the air inside the pod cavity. Compliance is not desired since it makes the system less responsive to controls.
Third, pods filled with blood increase the blood-plastic contact surface and create stagnant zones with low blood flow velocity that facilitate clot formation. Because the clots may form in the pods, the use of pods also necessitates the use of clot capture devices. Fourth, pod domes have a significant volume that increases the time that blood spends in contact with foreign materials. Altogether this increases the risk of blood loss, hypotension and clotting.
In order to address the needs of fluid removal and dialysis in acute emergency settings and to eliminate significant limitations of existing designs, it is believed that an improved sensor system should be adapted for use with dialysis machines. It is believed that the improved multiple sensor system disclosed herein can address these and other continuing needs.